<template>
  <ul class="list">
    <li class="item" v-for="item of letters"
    :ref="item"
    :key="item" @touchstart.prevent="handleTouchStart" @touchmove="handleTouchMove"
      @touchend="handleTouchEnd"
      @click="handleLetterClick">{{item}}</li>
  </ul>
</template>

<script>
  export default {
    name: 'CityAlphabet',
    props: {
      cities: Object
    },
    computed: {
      letters() {
        const letters = []
        for (let i in this.cities) {
          letters.push(i)
        }
        return letters
      }
    },
    data() {
      return {
        touchStatus: false,
        startY:0,
        timer:null
      }
    },
    // mounted() {
    //   this.startY = this.$refs['A'][0].offsetTop
    // },
    updated() {
      this.startY = this.$refs['A'][0].offsetTop
    },
    methods: {
      handleLetterClick(e) {
        this.$emit('change', e.target.innerText)
      },
      handleTouchStart() {
        this.touchStatus = true
      },
      handleTouchMove(e) {
        if (this.touchStatus) {
          if(this.timer){
            clearTimeout(this.timer)
          }
          this.timer = setTimeout(() => {
            const touchY = e.touches[0].clientY - 79
            const index = Math.floor((touchY - this.startY)/20)
            if(index>=0 && index < this.letters.length){
              this.$emit('change',this.letters[index])
            }
            this.timer=null
          },8)

        }
      },
      handleTouchEnd() {
        this.touchStatus = false
      }
    }
  }
</script>
<style lang="stylus" scoped>
  @import '~styles/varibles.styl'

  .list {
    display: flex;
    flex-direction: column;
    justify-content: center;
    position: absolute;
    top: 1.58rem;
    right: 0;
    bottom: 0;
    width: .4rem;
  }

  .item {
    text-align: center;
    line-height: .4rem;
    color: $bgColor;
  }
</style>
